Society's fascination with enclosed bodies of water reaches back to ancient times. As early as the 3rd millennium, B.C., a “great bath” was constructed and was perhaps the world's first swimming pool. Artificial swimming pools, ponds and fountains were popular in the ancient West and East alike, from Greeks, Romans, to Ancient Sinhalese. In fact, Roman emperors had private swimming pools in which fish also were kept, hence the Latin word for pool, “piscina”. In Ancient Sinhalese times, pools were decorated with flights of steps as well as “punkalas”, or pots of abundance, and scroll designs.
The fascination with man-made bodies of water remains strong today. For example, in some parts of the world, a swimming pool for private use is generally considered a status symbol (an indoor private pool, even more so). The private use of fountains, ponds and the like may also provide some correlation to status; however, these bodies of water are often generally incorporated in gardens and landscaping. Fountains, ponds, and/or reflecting pools associated with various government or historic places often become attractions in their own right. The reflecting pool in Washington, D.C., Trevi Fountain in Rome, and King Fahd's Fountain in Saudi Arabia are just a few of many famous examples.
Maintaining enclosed bodies of water, particularly those in areas where the water supply is mineral rich (i.e., “hard”), or bodies of water with frequent human contact can be difficult. As for bodies of water containing “hard” water, minerals and/or mineral deposits may accumulate on the sides of the enclosure for the water over time. As these minerals accumulate, both mechanical and aesthetic problems generally occur. Conventional mechanisms for removing unwanted mineral deposits in water body enclosures may prove to be both difficult and expensive. These mechanisms include sand blasting and scrubbing with pumice stones. Most conventional techniques require partial, if not complete drainage of the body of water. Particularly in areas of the country where water scarcity and drought conditions exist, this can be an expensive, environmentally unfriendly, or legally restrictive task.
Swimming pools are bodies of water that often have high levels of human use. It is therefore imperative that swimming pool water be maintained with very low levels of bacteria and viruses in order to prevent the spread of diseases and pathogens among users. Strong oxidizing agents are often used, especially simple chlorine compounds such as sodium hypochlorite. Other disinfectants include bromine compounds and ozone generated on site by passing an electrical discharge through oxygen or air. Chlorine may be supplied in the form of sodium hypochlorite solution, powdered calcium hypochlorite (“cal hypo”), cyanurated chlorine compounds (so called “stabilized” chlorine), or by dissolving chlorine gas directly in water. Maintaining a safe concentration of disinfectant is important for assuring the safety and health of swimming pool users. When any of these pool chemicals are used, it is important to keep the pH of the pool in the range of about 7.2 to 7.6. Higher pH dramatically reduces the sanitizing power of the chlorine due to decreased oxidation reduction potential, while lower pH causes user discomfort, especially to the eyes.
Where the water is sanitized by means of oxidizers, some suppliers of electronic monitoring equipment recommend that the efficacy of the oxidizer be measured by the oxidation-reduction potential of the water—a factor measured in millivolts, where the minimum acceptable oxidation reduction potential level in public pools is 650 millivolts. This is intended to ensure a 1-second kill rate for microorganisms introduced into the water. Unfortunately, a commonly used non-chlorine supplemental oxidizer, potassium monopersulfate, can produce measured 650 mV levels even in the absence of all sanitizing residuals. Cyanurated (“stabilized”) chlorinators can give falsely high chlorine readings when tested with OTO (ortho-tolidene, a yellow indicator dye used in inexpensive test kits), since the chlorine indicated by the dye is mostly in a combined form instead of free, and does not contribute to oxidation reduction potential. Oxidation reduction potential test cells are available as handheld instruments, and as probes for mounting permanently in the pool circulation plumbing to control automatic chlorine feeders.
Test kits to make basic measurements of free chlorine and pH from a sample of pool water, which are the most important items to control in a swimming pool, are packaged with small dropper bottles of reagents. These reagents are typically OTO for chlorine and phenol red for pH. The kits include vials for mixing a water sample with the test reagents, and color charts for reading the indicated levels. Besides chlorine and pH, which should be checked frequently, more sophisticated reagent kits provide tests for acid demand and base demand, total alkalinity (TA), calcium hardness, and cyanurate (“stabilizer”) concentration. These additional tests tend to vary only over weeks or months in a well-maintained pool, and thus need not be checked as frequently as chlorine and pH.
Pool sanitation, which necessarily involves toxic or mechanical means of killing microbes, can sometimes unintentionally irritate the users, especially if poorly maintained, such as when a high level of chlorine and/or low pH exists. Non-chlorine sanitizing chemicals and devices are promoted as being less harsh, but any sanitizer may have harsh unintended consequences if overused.
Water circulating through a pipe may be sterilized with UV light instead of chemicals, but some level of chemical sanitizer is still needed, because only a small portion of the pool water passes through the circulation system at any given time, and the circulation system typically only runs for a few hours each day. UV sterilization also does not inhibit algae from growing on pool surfaces, and it does not break down dissolved nitrogenous nutrients that feed algae growth. Accordingly, some type of oxidizing sanitizer is still generally needed to check these trends, although it need not be dosed during bathing hours for this purpose.
Generally, a well-managed pool will have no smell or taste, be scrupulously clean, and have crystal clear water. Most people would not want to swim in a pool that appears dirty even if germs were under control. A pool pump circulates water through a strainer and filter to remove dirt and other suspended particles. The plumbing circuit may also include a gas or electric heater, solar panels, and chemical injectors.
The proper management of a backyard swimming pool may be a difficult and time-consuming task. The chemical balance of the water has to be carefully monitored to make sure that it does not become fouled with algae or bacteria. Either of these will make the water smell and look unpleasant and can be a serious health hazard. The water must also be kept clear of debris such as fallen leaves and sticks, as these encourage fouling and become very slippery and dangerous as they start to decompose. Most people keep their pool either covered over or drained entirely during the months of the year in which it is not in use, as this is the easiest way to keep it sanitary (draining however can be a serious safety hazard with deeper pools and re-filling can be expensive in areas where water is scarce). Public and competitive swimming pools are therefore often, especially in colder climates, indoor pools—covered with a roof and heated—to enable their use all year round.
Chlorine may be generated on site, such as in saltwater pools. This type of system generates chlorine by electrolysis of dissolved salt (NaCl) using an electrical cell in the pool plumbing, instead of manually dosing the pool with chlorinating chemicals. Chlorine generators avoid the need for constant handling of sanitizing chemicals, and can generate sanitizing power at a lower cost than the equivalent chemicals, but they have a large up-front cost for the apparatus and for the initial loading of the pool with salt. The salt content gives the pool water a brackish taste, but not as salty as seawater. Pool water that splashes and evaporates, such as on a pool deck, leaves a salt residue. Being closer to isotonic salinity than fresh water, saltwater pools have an easier feel on the eyes, and a touch typically characterized as “silky”, not unlike bath salts.
For most swimming pools, regular (usually at least weekly) shock treatments are typically necessary to rid the pool of bacteria, lipids and other impurities. Common shock treatments include calcium hypochlorite. There are several disadvantages to weekly shock treatments, including that the chemical calcium hypochlorite is an extremely strong chemical, and can be harmful to contact with the skin, as well as if inhaled. Additionally, the use of chemicals requires swimming pool users everywhere to perform at-home approximate stoichiometry, which may prove difficult. Over time, people may become frustrated with the condition of their pool and decide that draining may be a better option to clean the pool enclosure, obtain “clean” water, and avoid the continuous use of harsh chemicals. Of course, draining a swimming pool can be an expensive, environmentally unfriendly, and enclosure-damaging proposition (as sometimes enclosures warp after the weight of the water is lifted).
While human contact with fountains, ponds and the like is less intense than that of swimming pools, there may still be a need to periodically rid these bodies of water of bacteria and/or algae build up. Of course, special consideration should be used in instances where these bodies of water contain wildlife, such as vegetation, fish, birds and/or the like.
There is a need for alternative mechanisms for impurity maintenance of enclosed bodies of water for mechanical, aesthetic and hygiene purposes.